Virtual desktop
Several desktop surfaces to switch between, so windows for different tasks don't end up in one heap.
The idea was laid out in Rooms, a 1986 research project by Austin Henderson and Stuart Card at Xerox PARC: work happens in contexts, and each context deserves its own set of windows. Unix picked it up early. vtwm and tvtwm, offshoots of twm, offered a desktop larger than the screen, and fvwm's pager showed a map of every workspace. CDE shipped with four workspaces as standard.
The big commercial systems took their time. macOS got Spaces in 2007, and Windows only gained built-in virtual desktops with Windows 10 in 2015 — nearly thirty years after Rooms.